Patent GB-274470-A (GB)
Title: Improvements in and relating to the automatic control of dynamo-electric machines
IPC: H02J3/42
Filed: 1927-07-12
Abstract: 274,470. British Thomson-Houston Co., Ltd., (Assignees of Hull, J. I.). July 15, 1926, [Convention date]. Systems depending on the use of two or more machines.-A control system for starting a single-phase synchronous motor by means of a mechanically coupled commutator repulsion motor comprises an automatic switch having contacts in the supply and field leads of the synchronous motor operated by a relay under the influence of two opposing forces in response to a condition which is proportional to synchronous speed, the relay being provided with a pair of opposed solenoids energized from the primary winding of the repulsion motor along axes at right angles, one axis being that of the commutator short-circuit. In a modification, a torque motor with a short circuited member performs the function of the solenoids. Fig. 1 shows the invention applied to the synchronizing operations in a, motor generator set comprising a continuous current generator 10 driven by a single phase synchronous motor 11; the set is started bv a repulsion motor 12. The field of the synchronous motor is supplied from the generator 10 through a switch 16 and a switch 21 carried loosely on the same plunger shaft is included in the main circuit. The switches are adapted to be actuated by solenoids 22, 23 under selected speed conditions proportional to the synchronous speed of the motor 11. As shown in Fig. 2, the coils 22, 23 are connected to the stator winding 18 of the motor 12, one 23 being in the axis of the short-circuited brushes and the other 22 at right angles thereto. The voltage across the coil 23 is proportional to the speed, and the voltage across the coil 22 is approximately constant or proportional to the slip plus the speed. At starting the switch 20 on the alternating-current side first connects with the contacts 27 in the repulsion motor circuit. The voltage across the solenoid 23 is zero at this instant aud the voltage across the coil 22 is a maximum whereby switches 21 and 16 are opened against the action of gravity. Further movement of the switch 20 connects the contacts 28 in the synchronous motor circuit with the supply. As the set approaches synchronous speed, solenoid 23 is energized and closes switches 21 and 16 in succession against the action of the solenoid 22 whereupon the synchronous motor 11 is connected for normal operation. The relay may control additional circuits, for example the field of the generator 10 or a resistance in the circuit of motor 12, and several similar relays differently adjusted may be employed. The starting motor may be left in circuit to assist in driving the set, and in conjunction with the relay, acts as a protective device to switch out the synchronous motor in case of overload. Fig. 3 shows a modified relay comprising a structure similar to polyphase induction motor and having a stator winding 31 and a squirrel cage rotor 32 rotatable through an angle determined by fixed contacts 34, 35 co-operating with an arm 33 on the rotor. Points on the winding 31 are connected to slip rings 30 connected to tappings 29 on the armature winding of the repulsion motor 12. At standstill and at synchronous speed no torque will be exerted on the, rotor 32 but at a predetermined proportion of synchronous speed, the arm will move on to contact 34, and at speeds above synchronism, the torque will reverse. In a modification the relav comprises a single phase rotor connected to the source through slip rings and driven from the motor shaft. The stator is a squirrel cage strueture which can be rotated through a small angle and has a contact arm co-operating with fixed contacts. The rotor winding of the relay may be of different pole number to the motor 12 and gearing may be interposed between the relay rotor and the motor so that the reversal of torque does not occur at synchronous speed. In a further modification the motor drives a converter having a single phase rotor connected through slip rings to the source and connected through a commutator to relay of the type shown in Fig. 3. The stator of the converter comprises a squirrel cage structure whereby a rotating field is set up at speeds other than synchronous speed or standstill. The squirrel cage structure may rotate. According to the Specification as open to inspection under Sect. 91 (3) (a) if polyphase motors are employed in the two last described modifications, a polyphase source of energy will be available for the relay so that the torque will not be zero at standstill and the squirrel cage structure in the converter of the last modification will be unnecessary. This subject-matter does not appear in the Specification as accepted.